How to use mTrigger Biofeedback after Muscle or Nerve Transfer Surgery

Injuries and patient cases that require muscle or nerve transfer surgery are often complicated and lengthy. The amount of time it takes for nerves to re-grow and re-innervate is nothing short of slow and cumbersome. Often patients will be in rehab for months or years yielding minimal progress. Sometimes a nerve reconstruction is not possible due to the extent of the injury, time since injury, or scarring.(1) In these cases, muscle transfer surgery can be considered. Very recent studies show, biofeedback can be a useful tool to help increase patient motivation and improve muscle activation and usage following such procedures.(1)

While a muscle transfer surgery can be performed in various locations and for a variety of reasons, we are going to focus on a case of using biofeedback following a gracilis transfer for reconstruction of the anterior deltoid.

The anterior deltoid muscle is innervated by the axillary nerve. Following surgical fixation of a proximal humeral fracture, there is a rare but potential complication for axillary nerve injury.(1) This can lead to anterior deltoid atrophy and functional loss of shoulder flexion strength and active range of motion for patients.(1)

Typically, a pectoral or latissimus dorsi muscle transfers is performed, but in this study a free gracilis muscle graph was used in hopes of improving anterior shoulder stability, flexion strength, and muscle bulk in the shoulder.(1) The graft was secured to the original anatomical landmarks, proximally at the lateral clavicle and distally to the deltoid tuberosity.(1) To establish reinnervation to the transferred muscle, a fascicle of the proximal axillary nerve just before it enters the quadrangular space is obtained.(1)

After the surgery, a rigorous physical therapy rehabilitation protocol is essential.(1,2) sEMG biofeedback such as the mTrigger device can be used to improve volitional muscle control and can be started as soon as the first signals are detected after reinnervation, typically 3-6 months post op. (1,2) Following this, biofeedback can be used as the patient works to decrease co-activation of the donor muscle, a common occurrence following this procedure.(1) With the help of sEMG biofeedback, the patient works to selectively activate the reinnervated muscle.(1) This also helps to reinforce the cognitive muscle activation separation.

In the case of muscle or nerve transfer surgery, biofeedback is critical for allowing patients to see muscle activation even when it exists at subclinical levels.(1) The mTrigger is perfect for this situation. Rehab providers can help to reinforce the cognitive aspect of the muscle firing by using biofeedback to promote motor learning and neuromuscular reactivation.(1)

A protocol following nerve transfer surgery is suggested by Sturma et al. The authors have broken it down into three phases.(2)

Phase 1: Use sEMG biofeedback to facilitate the initial movements after surgery.

During this phase, also called the silent phase, the goal is to improve cortical activation as the volitional activation of the reinnervated muscle can still take 3-6 months.(2) At this point, mirror therapy is a common intervention and can be used in conjunction with mTrigger biofeedback. Biofeedback is essential during this phase because it can be used before actual visible movements are possible to help with the cognitive load of establishing new motor patterns.(2)

Phase 2: Use sEMG biofeedback here to increase awareness of the new muscle.

This phase is when the first volitional activity is seen and can be confirmed by the sEMG signal repeatedly showing an amplitude of 2-3x higher than the amplitude during relaxation.(2) At this point, biofeedback is perfect for facilitating initial movements.

Phase 3: Use sEMG biofeedback to facilitate the separation of the target muscle during activities/exercises.

Now the patient can focus on relearning the new movement pattern of the transferred muscle (shoulder flexion in this case) instead of the previous nerve innervation motion.(2) For instance, elbow flexion without hand grasping. An example of a dual channel set up with the mTrigger device during this phase would be one channel on the reinnervated muscle and the second channel on the original donor muscle.

Summary
Practice, repetition, and structured training with biofeedback is critical after a muscle or nerve transfer surgery as recovery and reinnervation are occurring. The use of mTrigger biofeedback early on will help patients to stay motivated and working towards their goals even when progress is slow and muscle activation could not be detected otherwise.